Modal Verbs of Possibility | Impossibility | Expectation

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Modal verbs or semi-modals verbs such as can, could, may, might, should, would used as modal verbs of possibility, probability, impossibility, obligation, ability, wishes, expectation or advice in English grammar. In this lesson, we will learn different structures, rules, and examples of using modal verbs in different situation in order to express different meaning.


You need to learn the structures of modals of possibilty because you might get right forms of verbs based questions in your academic exams where you have to use the right forms of modal verbs based on the meaning of the sentences.

What are Modal Verbs?

In English grammar, modal verbs are the auxiliary verbs which are used in a sentence to express possibility, ability, request, advice or expectation. Can, could, may, might, should, would are known as modal verbs and they are used with a main verb in a sentence. When a modal verb is used with a verb in a sentence, it decorates the main verb with the impression of possibility, request or advice.

For an example, I help the people of this village.

When a modal verb ‘may/might’ used with the main verb in that sentence, it expresses the possibility of the action.

Example: I may help the people of this village. – (‘may help’ – possibility)


We have categorized this lesson into 3 sections. Now let’s learn about the use of modal verbs to express possibility, impossibility, and expectation in a sentence.

Types of Modal Verbs
Modal Verbs of Possibility
Modal Verbs of Impossibility
Modal Verbs of Expectation
3 Types of Modal Verbs

The modal verbs which are used to express possibility, probability, ability, duty or responsibilty in a sentence are known as modals of possibility. When we are confused about any action or event and we cannot tell certainly whether it will happen or not. But there is a possibility of happening, we will use the a certain structure to express such action or event.

Structure: can/could/may/might/should/would+ (base form of verb)

For examples,

  • He may buy this book today. – (Not sure of ‘buying books’)
  • I can wait for him here. – (Expressing possibility)
  • He might bring the book yesterday. – (Expressing possibility)
  • He could run fast in childhood. – (Expressing ability in past)
  • You should inform him the news. – (Expressing duty)
  • You might help him tomorrow. – (Expressing responsibility)

In order to express an action or event which is not possible to happen now but it could happen in the past, we use the structure of modals of impossibility. It expresses the possibility, wish, duty, and dream of past moment and now it is not possible to make it hapeen. All sentences which express such meanning or impression will be consided as modal verbs of impossibility.

Here is the structure, you should follow for such sentences:

Structure: could have/would have/should have+ (past participle form of verb)

Here are some examples:

If you had been an educated, you would have understood the matter.
(Expressing condition that is impossible to happen now)

You could have come here for him.
(Expressing past responsibility but it’s not possible now)

He should have invited you on his birthday.
– (Expressing the duty of past but it’s not possible anymore)

I wish if we could have won the match.
(Expressing impossible wish)

I should have done this work.

– (In this sentence, I am expressing the duty or responsibility by using the verbs ‘have done’. But, I am not sure whether I will do it or not.)


In order to express the possibility of happening any action or event in future, we count it as modals of expectation. Please note that the main point here is an event of future time which may happen or not. But, we are expecting that it is going to hapeen. For all of these sentences, we have to use the structure of modal verbs of expectation.



Lest + subject+ should+ base form of verb+ object


(it is desired/recommended/expected) +that+ subject+ should+ base form of verb+ object

For examples,

Take the umbrella with you lest it should rain in the afternoon.
(There is a possibility of raining in the afternoon. So, you are advised to take an umbrella for future protection)

It is desired that he should wait here for me.
– (You desire that he will wait in a place until you meet him)

If you want to test your skill in using the correct form of modal verbs, you can checkout this exercises sheet.

Summary: Modal Verbs

This is all about the use of modal verbs of possibility, impossibility, and expectation.


Except these specific impression, in case of all other general actions or events of present, past, or future will follow the general structure of tenses in English grammar.

For examples, see these sentences below:

  • I take tea in every morning. – (Present Indefinite Tense)
  • I am now writing a letter. – (Present Continuous Tense)
  • I have prepared my class lessons. – (Present Perfect Tense)
  • I have been reading the book for 2 hours. – (Present Perfect Continuous Tense)
  • You took the book for your last exam. – (Past Indefinite Tense)
  • They had collected the information for their project. – (Past Perfect Tense)

I hope you haven’t forgot the rules and strctures of indefinite tenses, continuous tenses, perfect tenses, and perfect continuous tenses.

Last of all, always try to undersstand the meaning and expression of sentences carefully and use the structures of modal verbs of possibility, impossibility or expectation if they match with the required expressions of feelings.